This invention relates to containers which hold media for use in detecting growth of microorganisms therein and more particularly concerns a multi-chambered module coordinated for use in an apparatus which assesses matabolic activity by monitoring the electrical, namely impedance, characteristics of nutrient media containing microorganisms.
A technique recently has been developed whereby growth of various types of microorganisms can be determined by measuring the changes of electrical properties of nutrient media containing the suspected microorganisms. For instance, in U.S. Pat. No. 3,743,581 changes in electrical conductivity of the medium indicate metabolic activity, whereas in U.S. Pat. No. 3,890,201 the growth or increase of microorganisms in a nutrient medium is correlated to the changes of impedance of the medium. Not only is metabolic activity determinable by the electrical characteristic method, but indications of quantity, identification, and antibiotic susceptibility are more rapidly achieved than by the previously known methods.
As the electrical measurement technique, especially in determining impedance changes, becomes more refined and automated, it becomes more critical to have a carrier or container for holding the nutrient media which is compatible with the progressions and advances of the techniques. In U.S. Pat. No. 3,743,581, for example, a basic media containing cell has been disclosed. For individual measurements the singular cell is acceptable, but newer apparatuses employing the impedance measuring technique are capable of monitoring many cells of growth media rapidly and accurately with individual recordings or computer analysis of each. In U.S. Pat. No. 3,890,201, an impedance measuring module has been taught which provides a plurality of individualized chambers for holding many samples of growth media. However, even in this plural-chambered module there are a number of deficiencies and shortcomings which indicate that there is room for further improvement.
To measure impedance changes of nutrient media the container contains at least two electrodes in contact with the media. An electrical signal passed through the electrodes allows the impedance of the media to be determined. The multiple chamber module previously mentioned includes metal conductors for electrodes on the top of a circuit board; with careless handling the exposed metallic strips may be readily damaged. Furthermore, long metallic leads extend to some of the chambers, thereby having segments with large areas of exposure; these long leads are subject to oxidation, fingerprints, scratches and other environmental conditions which may distort and unpredictably vary the reliability of the data being sought. Moreover, the individual chambers of the known plural-chambered module are attached directly over, and are resting on, the leads connected to the electrodes. This attachment scheme may not only damage the leads or interfere with their continuity, but also increases the chances of uneven placement of the chambers. Uneven placement of chambers undesirably increases the opportunity for media to escape and cross-contaminate media in other chambers.
Another shortcoming in the known plural-chambered module is that the individualized nature of the chambers (cylinders) precludes mass production methods. As the apparatuses for correlating microorganism growth with impedance changes of media become more sophisticated, there is a need for sufficient quantities of plural-chambered modules to justify mass production thereof for obvious economic reasons.